Preparation Method of Single-Ion Conductor-Sulfide Composite Solid Polymer Electrolyte

Abstract

The present invention relates to the technical field of lithium batteries, and discloses a preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte. In this composite electrolyte, a single-ion conductor polymer with a lithium ion transference number t Li + close to 1 is introduced, and it is first combined with a Li Li + GeP2S 10 sulfide solid electrolyte with a t 12 also close to 1 to form a composite electrolyte main structure with high lithium ion conductivity and high t Li + . Further, it is combined with a high-strength and ultra-thin PVDF-HFP-LiTFSI three-dimensional skeleton to construct a continuous filler-polymer interface in the composite electrolyte, thereby forming a continuous and through high-speed lithium ion transport path. The composite all-solid polymer electrolyte obtained by the present invention has comprehensive properties such as high lithium ion conductivity, high t Li + , high mechanical strength, and high electrochemical stability, and will comprehensively improve the overall electrochemical performance, energy density, cycle stability, and safety of lithium metal batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a composite solid electrolyte in a lithium battery. Background Art

[0002] Due to the high theoretical specific capacity (3860 mAh g -1 ) and low potential (-3.04 V) of lithium metal, and its advantages such as no memory effect and long cycle life, it is widely used in portable electronic devices such as mobile phones and laptop computers, as well as in smart grids, electric vehicles and other fields (J. M. Tarascon, M. Armand, Nature 2001, 414, 359). However, commercial lithium batteries with traditional liquid organic electrolytes have inherent safety hazards, such as leakage of toxic electrolytes, flammability and explosiveness, which limit their practical applications (A. Wang, D. Kong, S. Liu, K. Chiou, L. Zhi, J. Huang, Y. Xia, J. Luo, Adv. Mater. 2018, 30, 1703891). Developing polymer solid electrolytes to replace liquid electrolytes can effectively avoid the leakage problem and safety of traditional liquid lithium batteries, while effectively inhibiting the growth of lithium dendrites, and can greatly improve the cycle stability and energy density of lithium batteries.

[0003] Although polymer solid electrolytes have advantages such as light weight, good flexibility, strong processability, low cost, and simple preparation process, they still have problems such as low room-temperature ionic conductivity, low lithium-ion transference number, poor mechanical strength, poor thermal stability, difficulty in reducing thickness, and narrow electrochemical window, which limit their wide application in lithium metal batteries. (C. Wang, Y. Gong, B. Liu, K. Fu, Y. Yao, E. Hitz, Y. Li, J. Dai, S. Xu, W. Luo, E. D. Wachsman, L. Hu, Nano Lett. 2017, 17, 565). In view of this series of problems, researchers have proposed solutions from different angles, such as adding plasticizers, nano-fillers, block copolymers, etc. to polymer electrolytes. However, the above methods do not comprehensively solve the above problems. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the present invention provides a preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte. In this composite electrolyte, a single-ion conductor polymer with a lithium-ion transference number t Li + close to 1, and t Li+ Li close to 1 10 GeP2S 12 The sulfide solid electrolyte is used as the host material of the composite solid polymer and combined with the self-made ultra-thin and high-mechanical-strength PVDF-HFP-LiTFSI three-dimensional skeleton to prepare a single-ion conductor-sulfide composite solid polymer electrolyte with high ionic conductivity, high t Li + High, high mechanical strength, stable chemical properties and other comprehensive properties, while effectively improving the overall energy density, power density and safety of lithium metal batteries.

[0005] The object of the present invention is achieved as follows: A preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte, characterized by comprising the following steps:

[0006] Step 1) First, dissolve the single-ion conductor polymer in the NMP solution to obtain the NMP solution of the single-ion conductor polymer;

[0007] Step 2) Prepare an electrospinning solution by preparing a NMP solution of PVDF-HFP and LiTFSI and perform electrospinning;

[0008] Step 3) Place the three-dimensional skeleton nanofiber membrane obtained by electrospinning in a ventilated place to dry. After removing the solvent and drying, further heat-treat it in an argon atmosphere to obtain the PVDF-HFP-LiTFSI three-dimensional skeleton;

[0009] Step 4) Disperse the sulfide solid electrolyte powder in the NMP solution and obtain a uniform sulfide solid electrolyte-NMP dispersion by continuous stirring;

[0010] Step 5) Dropwise add the sulfide solid electrolyte-NMP dispersion to the NMP solution of the single-ion conductor polymer obtained in Step 1) under magnetic stirring. After mixing, continue magnetic stirring at room temperature to obtain a uniform single-ion conductor polymer-sulfide solid electrolyte mixture;

[0011] Step 6) Combine the single-ion conductor polymer-sulfide solid electrolyte mixture with the PVDF-HFP-LiTFSI three-dimensional skeleton by solution casting to obtain a preliminary single-ion conductor-sulfide composite solid polymer electrolyte. Remove the bubbles inside the single-ion conductor-sulfide composite solid polymer electrolyte by vacuum treatment and vacuum dry it at room temperature in a glove box, and then obtain the final single-ion conductor-sulfide composite solid polymer electrolyte film.

[0012] As a further limitation of the present invention, the single-ion conductor polymer in step 1) includes boric acid-based single-ion conductor polymers (characteristics such as quite high ionic conductivity, good thermal stability, simple preparation, low cost, environmental friendliness, etc.), sulfonic acid-based single-ion conductor polymers (the degree of negative charge delocalization of sulfonate anions (-SO3 − )) is higher than that of carboxylate anions, making Li + more likely to dissociate, which can significantly improve the lithium-ion transference number and lithium-ion conductivity of the solid polymer electrolyte). Among them, the mass concentration of the single-ion conductor polymer in the solution is 5% - 15%. Through experimental investigation, the single-ion conductor polymer solution within this mass concentration range is beneficial to the film formation of the subsequent single-ion conductor-sulfide composite solid polymer electrolyte.

[0013] As a further limitation of the present invention, step 2) is specifically as follows: Prepare an NMP solution by mixing polyvinylidene fluoride hexafluoropropylene PVDF-HFP and lithium bis(trifluoromethanesulfonyl)imide LiTFSI in a molar ratio of 20:1 to 25:1. Through experiments, it can be obtained that at this molar ratio, the single-ion conductor-sulfide composite solid polymer electrolyte can obtain a relatively high lithium-ion conductivity while taking into account relatively high mechanical strength, and its solid-liquid ratio is controlled at 1:15 to 1:25. Within this solid-liquid ratio range, the film formation of the single-ion conductor-sulfide composite solid polymer electrolyte is easier to operate during the preparation process.

[0014] As a further limitation of the present invention, step 3) is specifically as follows: Continue heat treatment at 200 ± 10 °C for 8 ± 0.5 h under an argon atmosphere to obtain a PVDF-HFP-LiTFSI three-dimensional framework.

[0015] As a further limitation of the present invention, step 4) is specifically as follows: Obtain a uniform sulfide solid electrolyte-NMP dispersion through continuous magnetic stirring, with the solid-liquid ratio controlled at 20% - 30%. The sulfide solid electrolyte is Li 10 GeP2S 12 , and at this solid-liquid ratio, Li 10 GeP2S 12 can be uniformly dispersed in NMP and will not introduce too much NMP solvent into the preparation process of the single-ion conductor-sulfide composite solid polymer electrolyte.

[0016] As a further limitation of the present invention, the addition amount of the sulfide solid electrolyte-NMP dispersion in step 5) is controlled such that the molar ratio of the sulfide solid electrolyte to the single-ion conductor polymer is 1:1 to 1:3. Through experimental tests, the single-ion conductor-sulfide composite solid polymer electrolyte obtained at this molar ratio has relatively high lithium-ion conductivity and lithium-ion transference number while maintaining relatively high mechanical strength.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] The present invention obtains a single-ion conductor-sulfide composite solid polymer electrolyte, and applies this composite polymer all-solid electrolyte to a lithium metal battery to improve the energy density, rate performance and safety of the battery.

[0019] In the single-ion conductor-sulfide composite solid polymer electrolyte prepared by the present invention, a single-ion conductor polymer with a lithium ion transference number tLi + close to 1 is introduced, which is first coupled with a Li10GeP2S12 sulfide solid electrolyte with a lithium ion transference number tLi+ also close to 1 to form a composite electrolyte main structure with high lithium ion conductivity and high tLi+, and further combined with a high-strength and ultra-thin PVDF-HFP-LiTFSI three-dimensional skeleton to construct a continuous filler-polymer interface in the composite electrolyte, thereby forming a continuous and through high-speed lithium ion transport path.

[0020] The present invention obtains a composite all-solid polymer electrolyte with high comprehensive properties such as high lithium ion conductivity, high tLi+, high mechanical strength, and high electrochemical stability, which will comprehensively improve the overall electrochemical performance, energy density, cycle stability and safety of the lithium metal battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0022] Figure 1 It is a scanning electron microscope picture of the single-ion conductor-sulfide composite solid polymer electrolyte of the present invention.

[0023] Figure 2 It is the test result of the lithium ion conductivity of the single-ion conductor-sulfide composite solid polymer electrolyte prepared by the present invention.

[0024] Figure 3 It is the test result graph of the lithium ion transference number of the single-ion conductor-sulfide composite solid polymer electrolyte of the present invention.

[0025] Figure 4 It is the specific capacity test result of the all-solid lithium metal-NCM811 battery assembled with the single-ion conductor-sulfide composite solid polymer electrolyte of the present invention and the all-solid lithium metal-NCM811 battery assembled with the ordinary polymer all-solid electrolyte at different rates. Detailed implementation mode

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0027] Example 1

[0028] A preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte includes the following steps.

[0029] Step 1) First, an appropriate amount of lithium tetrabutylborate single-ion conductor polymer of polytetramethylformate is dissolved in N-methylpyrrolidone (NMP) with a mass concentration of 5%.

[0030] Step 2) Polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) and LiTFSI are formulated into an N-methylpyrrolidone (NMP) solution according to a molar ratio of 20:1, and the solid-liquid ratio is controlled at 1:15 to prepare an electrospinning solution. The electrospinning conditions are set as follows: the voltage is 15.0 kV, the spinning speed is 0.5 mL / h, and the receiving distance is 22 cm.

[0031] Step 3) The three-dimensional skeleton nanofiber membrane obtained by electrospinning is placed in a ventilated place to dry. After removing the solvent, it is further heat-treated in an argon atmosphere at 200 °C for 8 h to obtain a PVDF-HFP-LiTFSI three-dimensional skeleton.

[0032] Step 4) Li 10 GeP2S 12 The sulfide solid electrolyte powder is dispersed in N-methylpyrrolidone (NMP), and a uniform sulfide solid electrolyte-NMP dispersion is obtained through continuous magnetic stirring. The solid-liquid ratio is controlled at 20%.

[0033] Step 5) The -NMP dispersion of the Li 10 GeP2S 12 sulfide solid electrolyte is added dropwise to the NMP solution of the lithium tetrabutylborate single-ion conductor polymer under magnetic stirring. The addition amount of the -NMP dispersion of the Li 10 GeP2S 12 sulfide solid electrolyte is controlled so that the molar ratio of Li 10 GeP2S 12 to the single-ion conductor polymer is 1:1. After mixing, continue magnetic stirring at room temperature for 4 h to obtain a uniform single-ion conductor polymer-Li10 GeP2S 12 Mixture solution

[0034] Step 6) Combine the lithium single-ion conductor polymer of butane borate lithium tetramethanoate - Li 10 GeP2S 12 The mixture solution is combined with the PVDF - HFP - LiTFSI three-dimensional framework by solution casting to obtain a preliminary single-ion conductor-sulfide composite solid polymer electrolyte. Remove the air bubbles inside the single-ion conductor-sulfide composite solid polymer electrolyte through vacuum treatment, and vacuum dry it at room temperature in the glove box for 12 h. Then raise the drying temperature to 180 °C and continue drying for 12 h to obtain the final single-ion conductor-sulfide composite solid polymer electrolyte film. The electron scanning electron micrograph of its surface is as shown in Figure 1 shown. The lithium single-ion conductor polymer of butane borate lithium tetramethanoate - Li 10 GeP2S 12 The composite solid electrolyte can reach 2.38×10 -2 ( Figure 2 )

[0035] Example 2

[0036] A preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte, comprising the following steps:

[0037] Step 1) Dissolve the lithium single-ion conductor polymer of butane borate lithium tetramethanoate in N-methylpyrrolidone (NMP) to form a stable solution, and control the mass concentration of the lithium single-ion conductor polymer of butane borate lithium tetramethanoate in the solution at 15%;

[0038] Step 2) The dissolution process of the lithium single-ion conductor polymer of butane borate lithium tetramethanoate adopts the magnetic stirring method, with a rotation speed of 500 r / min and a dissolution temperature of 80 o °C, and the stirring time is 5 h to obtain a stable NMP solution of the single-ion conductor polymer and keep it in a continuously stirred state for standby.

[0039] Step 3) Prepare an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride hexafluoropropylene (PVDF - HFP) and LiTFSI according to a molar ratio of 25:1, control the solid-liquid ratio at 1:25, and adopt the magnetic stirring method during the dissolution process, with a rotation speed of 500 r / min and a dissolution temperature of 80 o °C, and the stirring time is 5 h to obtain a stable NMP solution of the lithium single-ion conductor polymer of butane borate lithium tetramethanoate as the electrospinning solution and keep it in a continuously stirred state for standby.

[0040] Step 4) Electrospinning is carried out on the prepared electrospinning solution, and the electrospinning conditions are set as follows: the voltage is 15.0 kV, the spinning speed is 0.5 mL / h, and the receiving distance is 22 cm.

[0041] Step 5) The three-dimensional skeleton nanofiber membrane obtained by electrospinning is placed in a ventilated place for drying. After removing the solvent, it is further heat-treated at 200 °C for 8 h in an argon atmosphere to obtain an ultrathin and high mechanical strength PVDF-HFP-LiTFSI three-dimensional skeleton, which is stored in a glove box for standby.

[0042] Step 6) Li 10 GeP2S 12 The sulfide solid electrolyte powder is dispersed in N-methylpyrrolidone (NMP) in a glove box, and a uniform sulfide solid electrolyte-NMP dispersion is obtained through continuous magnetic stirring. The solid-liquid ratio is controlled at 30%, and continuous stirring is maintained for standby.

[0043] Step 7) The NMP dispersion of the Li 10 GeP2S 12 sulfide solid electrolyte is added dropwise to the NMP solution of the single-ion conductor polymer under magnetic stirring conditions. The addition amount of the NMP dispersion of the Li 10 GeP2S 12 sulfide solid electrolyte is controlled such that the molar ratio of Li 10 GeP2S 12 to the lithium tetrafluoroborate single-ion conductor polymer is 1:3. After mixing, continuous magnetic stirring is continued at room temperature for 4 h to obtain a uniform lithium tetrafluoroborate single-ion conductor polymer-Li 10 GeP2S 12 mixture. This process is carried out in a glove box, and the obtained lithium tetrafluoroborate single-ion conductor polymer-Li 10 GeP2S 12 mixture is continuously stirred in a glove box for standby.

[0044] Step 8) In the glove box, the single-ion conductor polymer-Li 10 GeP2S 12 mixture is combined with the ultrathin and high mechanical strength PVDF-HFP-LiTFSI three-dimensional skeleton by solution casting to initially obtain a single-ion conductor-sulfide composite solid polymer electrolyte. The air bubbles inside the single-ion conductor-sulfide composite solid polymer electrolyte are removed by vacuum treatment in the glove box, and it is vacuum dried at room temperature for 12 h in the glove box. Then, the drying temperature is raised to 180 °C and drying is continued for 12 h to obtain the final single-ion conductor-sulfide composite solid polymer electrolyte, whose lithium ion transference number reaches 0.91 (Figure 3 ).

[0045] Example 3

[0046] A preparation method of a single-ion conductor-sulfide composite solid polymer electrolyte, comprising the following steps:

[0047] Step 1) First, dissolve the PVDF-HFP-g-AMPSLi single-ion conductor polymer in N-methylpyrrolidone (NMP) to form a stable solution, and control the mass concentration of the PVDF-HFP-g-AMPSL single-ion conductor polymer in the solution at 10%;

[0048] Step 2) The dissolution process of the PVDF-HFP-g-AMPSL single-ion conductor polymer adopts the magnetic stirring method, with a rotation speed of 500 r / min and a dissolution temperature of 80 o °C, and the stirring time is 5 h, thus obtaining a stable NMP solution of the single-ion conductor polymer and keeping it under continuous stirring for standby;

[0049] Step 3) Prepare an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) and LiTFSI according to a molar ratio of 23:1, control the solid-liquid ratio at 1:20, and adopt the magnetic stirring method during the dissolution process, with a rotation speed of 500 r / min and a dissolution temperature of 80 o °C, and the stirring time is 5 h, thus obtaining a stable NMP solution of the single-ion conductor polymer as the electrospinning solution and keeping it under continuous stirring for standby;

[0050] Step 4) Electrospin the prepared electrospinning solution, and set the electrospinning conditions as: voltage 15.0 kV, spinning speed 0.5 mL / h, and receiving distance 22 cm;

[0051] Step 5) Place the three-dimensional skeleton nanofiber membrane obtained by electrospinning in a ventilated place for drying. After removing the solvent, further heat-treat it at 200 °C in an argon atmosphere for 8 h to obtain an ultra-thin and high-mechanical-strength PVDF-HFP-LiTFSI three-dimensional skeleton, and store it in a glove box for standby;

[0052] Step 6) Disperse the Li 10 GeP2S 12 sulfide solid electrolyte powder in N-methylpyrrolidone (NMP) in a glove box, and obtain a uniform sulfide solid electrolyte-NMP dispersion through continuous magnetic stirring, control the solid-liquid ratio at 25%, and keep continuous stirring for standby;

[0053] Step 7) The Li 10 GeP2S 12The -NMP dispersion of the sulfide solid electrolyte was added dropwise to the NMP solution of the single - ion conductor polymer under magnetic stirring. Li 10 GeP2S 12 The addition amount of the -NMP dispersion of the sulfide solid electrolyte was controlled such that the molar ratio of Li 10 GeP2S 12 to the single - ion conductor polymer was 1:2. After mixing, magnetic stirring was continued at room temperature for 4 h to obtain a homogeneous single - ion conductor polymer - Li 10 GeP2S 12 mixed solution. This process was carried out in a glove box, and the obtained single - ion conductor polymer - Li 10 GeP2S 12 mixed solution was continuously stirred in the glove box for standby;

[0054] Step 8) In the glove box, the single - ion conductor polymer - Li 10 GeP2S 12 mixed solution was combined with an ultra - thin, high - mechanical - strength PVDF - HFP - LiTFSI three - dimensional framework by solution casting to preliminarily obtain a single - ion conductor - sulfide composite solid polymer electrolyte. Bubbles inside the single - ion conductor - sulfide composite solid polymer electrolyte were removed by vacuum treatment in the glove box, and it was vacuum - dried at room temperature in the glove box for 12 h. Then, the drying temperature was raised to 180 °C and drying was continued for 12 h to obtain the final single - ion conductor - sulfide composite solid polymer electrolyte.

[0055] Using this all - solid polymer electrolyte containing a vertical array framework to assemble an NCM811 - lithium all - solid - state battery, compared with a common PVDF polymer all - solid - state electrolyte, it has very remarkable cycle stability (attached Figure 4 ).

[0056] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a single ion conductor-sulfide composite solid polymer electrolyte, characterized in that: The steps include: Step 1) firstly dissolving a single ion conductor polymer in a NMP solution to obtain an NMP solution of the single ion conductor polymer, wherein the mass concentration of the single ion conductor polymer in the solution is 5% to 15%, and the single ion conductor polymer includes a boric acid type single ion conductor polymer and a sulfonic acid type single ion conductor polymer; Step 2) preparing NMP solution with PVDF-HFP and LiTFSI to prepare electrospinning solution for electrospinning; Step 3) placing the three-dimensional skeleton nanofiber membrane obtained by electrospinning in a ventilated place for drying, removing the solvent and drying, and further heat treating in an argon atmosphere to obtain a PVDF-HFP-LiTFSI three-dimensional skeleton; Step 4) dispersing the sulfide solid electrolyte powder in the NMP solution, and obtaining a uniform sulfide solid electrolyte-NMP dispersion by continuous stirring, specifically: obtaining a uniform sulfide solid electrolyte-NMP dispersion by continuous magnetic stirring, the solid-liquid ratio is controlled at 20% to 30%, and the sulfide solid electrolyte is Li 10 GeP2S 12 ; Step 5) adding the sulfide solid electrolyte-NMP dispersion dropwise to the NMP solution of the single ion conductor polymer obtained in step 1) under magnetic stirring, and continuing magnetic stirring at room temperature after mixing to obtain a uniform single ion conductor polymer-sulfide solid electrolyte mixed solution; Step 6) The single ion conductor polymer-sulfide solid electrolyte mixture is combined with the PVDF-HFP-LiTFSI three-dimensional skeleton by solution casting to obtain a preliminary single ion conductor-sulfide composite solid polymer electrolyte, and the bubbles inside the single ion conductor-sulfide composite solid polymer electrolyte are removed by vacuum treatment, and vacuum dried at room temperature in a glove box to obtain the final single ion conductor-sulfide composite solid polymer electrolyte film.

2. The method for preparing the single ion conductor-sulfide composite solid polymer electrolyte according to claim 1, characterized in that: Step 2) is specifically as follows: polyvinylidene fluoride hexafluoropropylene PVDF-HFP and lithium bis(trifluoromethylsulfonyl)imide LiTFSI are prepared into an NMP solution at a molar ratio of 20:1 to 25:1, and the solid-liquid ratio is controlled at 1:15 to 1:

25.

3. The method for preparing the single ion conductor-sulfide composite solid polymer electrolyte according to claim 1, characterized in that: Step 3) is specifically as follows: heat treatment is continued at 200±10°C for 8±0.5h under an argon atmosphere to obtain a PVDF-HFP-LiTFSI three-dimensional skeleton.

4. The method for preparing the single ion conductor-sulfide composite solid polymer electrolyte according to claim 1, characterized in that: In step 5), the amount of -NMP dispersion of the sulfide solid electrolyte added is controlled so that the molar ratio of the sulfide solid electrolyte to the single ion conductor polymer is 1:1 to 1:3.

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